Problem: Michael ate 1 slice of cake. Emily ate 3 slices. If Michael ate $\dfrac{1}{7}$ of the cake, what fraction of the cake is remaining?
Explanation: If 1 slice represents $\dfrac{1}{7}$ of the cake, there must have been a total of 7 slices. $\text{fraction of cake remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 4 slices, which leaves 3 out of 7 slices remaining. There is $\dfrac{3}{7}$ of the cake remaining.